remove prefer-dynamic helper

Author: Oneirical

tests/run-make/same-lib-two-locations-no-panic/rmake.rs

@@ -14,9 +14,9 @@ fn main() {
     let tmp_dir_other = tmp_dir().join("other");
 
     fs::create_dir(&tmp_dir_other);
-    rustc().input("foo.rs").crate_type("dylib").prefer_dynamic().run();
+    rustc().input("foo.rs").crate_type("dylib").arg("-Cprefer-dynamic").run();
     fs::rename(dynamic_lib("foo"), &tmp_dir_other);
-    rustc().input("foo.rs").crate_type("dylib").prefer_dynamic().run();
+    rustc().input("foo.rs").crate_type("dylib").arg("-Cprefer-dynamic").run();
     rustc().input("bar.rs").library_search_path(&tmp_dir_other).run();
     fs::remove_dir_all(tmp_dir());